Protective device for alternating-current circuits.



L. ANDREWS. PROTECTIVE DEVICE FOR ALTBRNA'TING CURRENT CIRCUITS.

APPLIOATIOII FILED SEPT. 18. 1905..

Fig.1.

Inventor.

PATENTED OCT. 16, 1906.

UNITED STATES PATENT OFFICE.

LEONARD ANDREWS, OF MANCHESTER, ENGLAND, ASSIGNOR TO STANLEY G. I. ELECTRIC MANUFACTURING COMPANY, A CORPORAT ON OF MAS- SACHUSETTS.

PROTECTIVE DEVICE FOR ALTERNATlNG-CURRENT CIRCUITS.

Specification of Letters Patent.

Patented Oct. 16, 1906.

Application filed September 18, 1905- Serial No. 278.863-

alternating-current circuits from a reversal. of energy therein and its ob ect is to provide.v

protecting means which shall be simple and at the same time reliable under all conditions.

It has been proposed heretofore to arrange reverse-current protective devices with two windings, one connected in series with the main circuit to be protected and the other in shunt to that circuit, and to superpose the two windings on each other either in a solenoid or on a transformer-core, the resultant magnetic effect of the two windings being utilized to secure the operation of the device u on a relative reversal of current-flow.

hen such an arrangement is used with alternating-current circuits, a heavy reverse current in the series coil may completely wipe out the effect of the potential-coil, inducing in the potential-coil by transformer action an electromotive force which renders the device inoperative. may prove unreliable in the case of a short circuit, where its operation-is most needed.

By combining the effects of the shunt and se- Since the series and shunt windings are en-- tirely separate, no transformer action between the two is possible.

My present invention consists in an 'improvement in the arrangement disclosed in my former patent and renders the apparatus still more reliable for all conditions.

One feature of myinvention consists in ar ranging the series transformer with a core Thus such a device adapted to be saturated by an overload-current, so that the current supplied to the local circuit of the series transformer can never exceed a redetermined amount, and I also connect t e series and shunt transformers to the local circuit in such a manner that each current is supplied to the local circuit at points equipo'tential with respect to the other transformer. By adapting the core of the series transformer for saturation on overload an undue preponderance in the effect of the series current is avoided, and b equipotential with respect to each other they are made entirely independent of each other in their effect u on. the rotective device.

I have found t at on or certainconditions protection is required not only against a true reversal of energy in the main circuit, but also against ,a heavy flow of wattless current. Thus, for instance, in the case of an alternating-current generator connected in arallel with other machines in case of the failure of a prime mover that generator will run as a motor, driving the prime-mover, and a true ;reversal of energy Wlll occur in the leads. con

necting the generator to the bus-bars. For such contingency a protective device 0 erating upon a reversal of ener will affor adequate protection; but if t e field-circuit-of the generator is broken while the prime mover remains undisturbed a different condition' exists. Although the generator-armature inonesense acts as a shortcircuit on the bus-bars, on the other hand the rime moverfis still attempting to do work, or as long as the generator remains in synchronism the governor of the prime mover cannot act to cut off the supply of steam or water, so that while, on the one hand, there; is a tendencyfor energy to pass from the bus-bars to the armature, as to a short circuit, onthe other hand there is a tendency, due :teitfiepower delivered from-the primeniover toQ-the/generator, for thev generator tosupply energy to the bus-bars! The result :is that a very heavy synchronizing-current passesbetween the generator and the bus-bars. 'This ourrent is a leading" current with res ect to the faulty enerator and serves to nish the magnetization ofthe machine and to hold' t in synchrmiisrn, while as regards the other su plying the two currents at points in the oca circuit cuit, but displace the phase of one of these rangement of protective devices embodying short circuit.

'direction and the other instant in the other,

- rents dependent in phase on the current and the rent. This may be accomplished by arrangterminals of which are connected to the tergenerators connected to the bus-bars this current is a. lagging current. The energy transferred through the leads from the generator to the bus-bars is one instant in one direction. Consequently there is no true reversal of energy, and a device operative only u on a reversal of energy will not serve to cut t e generator out of circuit. In order to meet this contingency, as well as that of a true reversal of energy, I provide-two magnet-windings each arranged in a local closed circuit and supply to each circuit two 'curon the voltage, respectively, on the main circurrents in one circuit relative to thesame current in the other circuit, and provide means controlled by either magnet-winding for opening the main circuit. l Vith'this arrangement one of the magnet-windings may be caused to operate upon a true reversal of ener and the other upon the flow of a heavy watt ess current, and since the operation of either device opens the circuit adequate protection is given for all conditions.

My invention will best be understood by reference to theaccompanying drawings, in Which' l Figure 1 shows diagrammatically an army invention. Fig. 2 shows a view of the series transformer, and Fig. 3 shows acrosssectional view of one of the relays.

In the drawings, A represents an alternating-current generator connected to the bus-v bars B. It is assumed that it is desired to protect the generator against a reverse flow of energy from the bus-bars and also against a heavy flow of wattless current.

0 represents a circuit-breaker inserted in generatorleads and provided with a tri ping-coil c. l

represents a transformer the primary winding of which, d, is inserted in series with the generatordeads. The transformer is shown rovided with two secondary windings d and The core of the transformer is arranged to be saturated by an overload-curing a portion of the core with areduced crosssection, as clearly shownin Fig, 2, or the whole core may be given a cross-section ada ted to be saturated on overload. If pre erred, the core may be arranged 'to be saturated on less than a-full load. It is only essential, however, that it. should become saturated on an overload, so as to prevent the secondary current from rising a great amount above its normal value in case of a M M represent two "magnet-windings,the

minals of the secondary windings d and (Z While have shown two ndependcnt secondcoil 0 and battery b.

.and WOUlt extent in both parts of the winding. The deary windings on the transformer D, it is obvious that a single secondary winding may be employed and both magnet-windings con nected to the single transformer-winding, if

preferred.

E represents a shunttransformer having its primary connected to the bus-bars. One

terminal'of the secondary is'connectedto the middle points of both magnet-windings M and M while the other terminal of the sec-' ondary is connected to the middle points of the series-transformer. windings d and d It will be seen that this connection from the shunt-transformer to each local circuit is at passes from the middle of the winding outward to both terminals. The secondary windings d. and (1 through which these currents pass, serve as differential choke-coils to maintain the currents from the shunt-transformer balanced in the two parts of the magnet-windin Consequentlythe two currentsassist eac other in one half the winding and oppose each other in the other half.

Thus, for instance, if normallythe two currents in the magnet-winding M are in phase and assist each other in the lower half of the winding and oppose each other in the upperv half there will be no tendency for the magnet to raise its core, but, on the contrary, to

hold it in the position shown in Figs. 1 and Now if the relative phase of the current from the series transformershould be shifted one hundred and eighty degrees the two cur-- rents would assist each other in the. upper half of the winding and oppose'each other in the lower half. The magnet-winding would consequently raise its core, raisin the switchcontact m and closing a circuit throu h tripcuit-braker C, and protection would consequently be afforded against a reversal of energy. If, however, the two currents in the The circuit of te generator 'A would thus be opened by the cirmagnet M were normally in phase with a non-inductive load upon the generator A, a difference in phase of only ninety degrees in the current from the series transformer would be produced by a flow of wattless current in the generator-leads. The two currents in the magnet-winding would then be ninety de rees out of phase with each other Tmerely assist each other to a slight" vice consequently would beinoperative. If,

on the other hand, the two currents in the winding M were ninety degrees out of phase with each-other on a non-inductiveloafi n the generator, it is evident that a flow of wattless current in the generator-leads, which would shift the current from the series transformer ninetv degrees, would bring the two currents in the winding M into opposition in one half of the winding and into the same phase in the other half, so that the devices if properly innected would operate to open the generator-circuit. In order to secure this operation on either a true reversal of energy or a flow of wattless current, I pro- Vide two windings M and M and relatively displace the phases of the currents supplied to these winnings from the potential-transformer E. This is readily accomplished by inserting a non-inductive resistanceR in the connection. between the transformer E and one of the windings and an inductive resistance I in connection to the other winding adapted to lag the current b an angle between forty-five and ninety egree's. With this arrangement the winding M will operate to open the generator-circuit upon a true reversal. of energy, while the ma net M will operate upon the flow of watt ess current. Consequently the generator protected against all contingencies that can arise.

I do notdesire to limit myself to the particular construction and arrangement of parts here shown, but aim in the appen dcd claims to cover all modifications which are within the scope of my invention.

I'Vhat I claim as new, and desire to secure by Letters Patent of the United States, is

1. In a protective device, in combination with a main alternating-current circuit, a transformer having its primary in series with said circuit and having a core adapted to be saturated by an overloadmurrent in said on 40 ,cuit, an electroresponsive device connected n a local closed circuit with the secondary of said transformer, and connections from equipotential points in said circuit to a source of voltage dependent in phase upon the voltage of the main circuit.

2. In a protective device, in combination with a main alternating-current circuit, a shunt-transformer, a series transformer having a core adapted to be saturated by an overload-current in said circuit, andan electroresponsive device connected in a local closed circuit with the secondaries of both transformers, one transformer being connected to equipotential points with respect to the other transformer.

3. In a rotcctive device; in combination with a main alternating-current circuit, a transformer having its primary in series with said circuit-and having a core adapted to be saturated by an o'verloadcurrent in said ciredit a magnet-wlnding connected in a local closed circuit with the. secondary of said transformer, connections from equipotcntial ointsin saidcircuit to a source of voltage pendent in upon the voltage of the main circuit, and a switch controlled bysaid magnet-winding and adapted to open the main circuit.

4. In a protective device, in combination with an alternating-current circuit, a shunttransform r, a series transformer having a core adapted to be saturated by an overloadcurrent in said circuit, a magnet-winding connected in a local closed circuit with the secondaries of both transformers, one transformer being connected to equipotential points with respect to the other transformer, and a switch controlled'by said magnet-winding adapted to open the main circuit.

5. In a protective device, in combination with a main alternating-current circuit, a transformer having its primary in series with said circuitand having a core adapted to be saturated by an overload-current in said circuit, a magnet-winding having its terminalsconnected to the secondary terminals of said transformer, connections from an intermediate point on said winding to one terminal of a source of voltage dependent in hase upon the voltage of the main circuit and from both terminals of said winding tothe other termi-' nal of said source, and means controlled by said winding for opening'the main circuit. I

6. In a protective device, in combination with a main altemating-current circuit, a shunt-transformer, a series transformer having a core adapted to be saturated by an over- 'loadcurrent in said circuit, a magnet-winding connected in a local closed circuit with the secondaries of both transformers, one of said secondaries being connected to the terminals of said winding and the other to intermediate points on said winding and on the first secondarv respectively, and means controlled by said winding for opening the main circuit.

7. In a protective device, in combination with a main alternating-current circuit, a transformer having its primary in'series with said circuit, two magnet-windings connected in local closed circuits with the transformer secondary, means for impressing on said local circuits respectively two voltages both dopendent in hase onthe voltage of the main circuit but (iifl'erin in phase from each other, and means controll ed by either magnet-winding for opening the main circuit.

8. In a protective device, in combination with a main alternating-current circuit, two magnet-windings each connected in a local closed circuit, means for roducing in each local circuit two currents ependent in phase on the current and volta e respectively'of the main circuit, one of said currents being of different phase in thetwo local circuits, and means controlled by either magnet-winding for opening the main circuit.

9. In a 1.- otective device, in combination 'with a main alternating-current circuit, a shunt-transformer, a series transformer, two

magnet-windings each connected in a local closed circuit with the secondaries of both transformers, one of. said secondaries being connected to points in each local circuit equ1- potential with-respect to the other secondary, means for displacing the relative phases of the currents in said local circuits from one transformer, and means'controlled by either magnet-winding for opening the main cir cuit.

10.. In a protective device, in combination with a main alternatlng-current circuit, a

transformer having itsprimary in series with said circuit; two-magnet-windings having their terminals connected to the secondary terminals of said transformer, connections from intermediate points of both windings to; one terminal of a source of voltage'dependentin phase upon the voltage ofthe main circuit, a connection from an intermediate point on said transformer secondary to the other 'terminal of said source, means? for relatively displacing the currents supplied to said two windings from said source, 'and means con trolled by either winding for opening the main circuit.

and means controlled by either magnet-' winding for opening the main circuiti 12. In a rotective device, in combination -with a main alternating-current"circuit, a

transformer ha ving its primary in series with said circuit and having a core adapted to be saturated by an overload-current in said cir-H c'uit, two magnet-windings connected in local closed circuits with the transformerhand this 16th secondary, mean,s for impressing on each of said local circuits at points equipotential with respect to said transformer-secondary a voltage dependent in phase upon the voltage of the main circuit,' the voltages imp'ressed on the two local circuits being of different phase,

and means controlled by either magnetw'inding for opening the main circuit.

13. In a protective device, the combination with a main alternating-current circuit,

a shunt-transformer, a series transformer,

two magnet-windings each connected in a v local closed circuit to the secondaries of both transformers, one of. said secondaries being connected to polnts in each local circuit equipotentlal with respect to the other secondary,

a non-inductive resistance inserted in the connection between one of sa1d secondaries and one of'the' local circuits, an inductive resistance inserted in the connection between Y saidsecondary and the other local'eircuit,

and means controlled by either magnetwinding for opening the main circuit.

14. In a protective device, the combination with a main, alternating-current circuit, a transformer having itsprimary in series with saidcircuit, two magnet windings ha v'- .ing their terminals connected to the secondary terminals of said transformer, a transformer having its primary in shunt to said main circuit, connections from one secondary. terminal of sa1d shunt-transformer to mtermediate I points on both magnet-windings, inductive and non-inductive resistances inserted respectively 1n sa1d connections, a connectlon from the other secondary terminal of the shunt-transformer to an intermediate point on the series-transformer-secondary, and

. means controlled by either magnet-winding for opening the main circuit.

In witness whereof I have hereunto set my dayiof August, 1905; -LEONARD ANDREWS. Witnesses: l v

, GEORGEH. FAwoUs,

JOSEPH DRUMMOND. 

